1. Field of the Invention
The present invention relates to a transistor and an organic light emitting diode display, and more particularly, to a transistor that produces a driving current with high uniformity despite deviations in manufacturing processes, and an organic light emitting diode display employing the transistor.
2. Discussion of Related Technology
Organic light emitting diode displays (OLEDs) are emissive displays that electrically excite fluorescent or phosphorescent organic compounds to emit light. OLEDs have been identified as next generation displays that can advantageously be driven with low voltage, and the displays can be thin with a wide viewing angle and fast response speed, thereby solving problems associated with liquid crystal displays (LCD).
OLEDs are classified into active matrix (AM) (hereinafter, referred to as “active driving”) OLEDs and passive matrix (PM) OLEDs according to the driving method employed. An exemplary active driving OLED is illustrated in FIGS. 1A and 1B, wherein each pixel 10 includes two thin film transistors (TFT) M1 and M2 and a storage capacitor C. The two TFTs M1 and M2 function as a switching transistor M1 configured to control the operations of the pixels, and a driving transistor M2 configured to drive an electroluminescent (EL) device.
The driving transistor M2 includes a drain region and a source region formed by doping a substrate with high concentration impurities, a semiconductor layer having a channel region formed between the drain region and the source region, a gate insulating layer formed on the semiconductor layer, and a gate electrode formed on the channel region of the semiconductor layer with the gate insulating layer interposed. The driving transistor M2 further comprises a drain electrode and a source electrode positioned on the gate electrode and connected to the drain region and the source region through contact holes, with an inter-insulating layer interposed.
During manufacture, the semiconductor layer of the driving transistor M2 is crystallized by a laser beam 20 that proceeds in a first direction. This process may generate a high concentration defect in the source region or the drain region connected to the contact holes of the driving transistor M2. The defect part may be generated due to unexpected non-uniform distribution of energy in laser beams of nearly the same timing. The high concentration defect prevents current flow from the source region to the drain region. Thus, deviations in the driving transistor manufacturing processes result in reduced uniformity in the current transmission characteristics of driving transistors.
In some OLEDs, various compensating circuits are employed to prevent picture quality deterioration and to improve display uniformity. However, when compensating circuits are employed in the OLED, the complexity of the pixels is increased, numerical aperture (NA) deteriorates, and yield of the OLED is reduced.